Heat Exchange Device with Variable Tube Material

ABSTRACT

A heat exchange device utilizing variable tube materials is provided. In one particular embodiment, the heat exchange device is an evaporative condenser with a multi-pass tube bundle. The first few tube passes (typically 1-3 tube passes) of the tube bundle, which in operation are typically exposed to superheated refrigerant gas, are comprised of a material that is highly resistant to corrosion (e.g., 316/316L stainless steel). The remaining tube passes, which in operation are typically exposed to a lower-temperature refrigerant (i.e., saturated two-phase or subcooled liquid), are comprised of one or more lower-cost, less corrosion-resistant material (e.g., 304/304L stainless steel).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional U.S. Patent ApplicationNo. 62/164,174, filed on May 20, 2015, which is incorporated herein inits entirety by reference. In addition, Provisional U.S. PatentApplication No. 62/023,939, filed on Jul. 13, 2014, is also incorporatedherein in its entirety by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTIONS

1. Technical Field

The embodiments described and claimed herein relate generally to a heatexchange device with improved corrosion resistance. In one embodiment,the inventions include the use of at least two different tube materialswith varying degrees of corrosion resistance in an air-to-refrigerantheat exchanger (e.g., evaporative condenser) tube bundle section.

2. Background Art

It is common in the refrigeration industry to use 304/304L stainlesssteel for heat exchanger tube bundles for reasons of cost, easyfabrication, and durability. However, it is well known that tube bundlesthat are fabricated using 304/304L stainless steel, without propertreatment and maintenance, are vulnerable to corrosion and subsequentpitting. Corrosion can be especially prevalent in evaporative condenserapplications in the first few tube passes at the inlet of the heatexchanger, due to the high temperature of the entering, superheatedrefrigerant. For example, when using ammonia as a refrigerant, thetemperature of the entering superheated refrigerant typically reaches120-165° F. before cooling to a saturation temperature of approximately95° F. after the first couple of tube passes. Thus, the risk ofaccelerated corrosion is higher in the first few tube passes due to thehigher temperature of the refrigerant. It is well known that materialssuch as 304/304L stainless steel become more susceptible to corrosionwith increases in temperature, especially when exposed to the chloridesand chlorines commonly used to treat the recirculated evaporative fluid(e.g., water).

In practice, it is known that some operators do not regularly treat ormaintain their heat exchange devices. Thus, there are several methodsthat are used in the art to inhibit corrosion. One option is to increasethe wall thickness to increase the tube life. Another option is to avoiduse of 304/304L stainless steel in favor of 316/316L stainless steel.Both of these options, however, come with increased material andfabrication costs.

BRIEF SUMMARY OF THE INVENTIONS

The embodiments described and claimed herein solve at least some of theproblems of the prior art.

In one particular embodiment described and claimed herein, at least twodifferent materials are used to fabricate the tube bundle for a heatexchanger. The material having greater resistance to corrosion is usedfor the tube passes that are exposed to higher temperature refrigerant,while the material having lower cost and/or durability is used for thetube passes that are exposed to lower temperature refrigerant. Thenumber of tube passes using the higher-corrosion-resistant material willdepend upon the application. For example, the number of tubes requiringhigher-corrosion-resistant material may vary depending upon therefrigerant and type of heat exchanger, among other factors. As just oneof many examples, for an evaporative condenser application using ammoniaas a refrigerant, 316/316L stainless steel could be used for the firstone to two tube passes, while 304/304L stainless steel could be used forthe remaining tube passes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other features, aspects, objects, and advantages of theembodiments described and claimed herein will become better understoodupon consideration of the following detailed description, appendedclaims, and accompanying drawings where:

FIG. 1 is a perspective view of a first embodiment of a tube assemblyfor an evaporative condenser;

FIG. 2 is a front view of the first embodiment;

FIG. 3 is a top view of the first embodiment;

FIG. 4 is a right side view of the first embodiment;

FIG. 5 is a sectional view along plane A-A shown in FIG. 3; and,

FIG. 6 is a magnified view of the upper region of the section view ofFIG. 5.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the embodiments described and claimed herein or which render otherdetails difficult to perceive may have been omitted. It should beunderstood, of course, that the inventions described herein are notnecessarily limited to the particular embodiments illustrated. Indeed,it is expected that persons of ordinary skill in the art may devise anumber of alternative configurations that are similar and equivalent tothe embodiments shown and described herein without departing from thespirit and scope of the claims.

Like reference numerals will be used to refer to like or similar partsfrom Figure to Figure in the following detailed description of theinventions.

DETAILED DESCRIPTION OF THE INVENTIONS

In FIGS. 1-6, a first embodiment of tube bundle for a heat exchangedevice 10 is provided with a closed loop, indirect heat exchange methodinteractive with an external, direct evaporative heat exchange method.In tandem, these two methods working simultaneously enable heatabsorption from an internal, closed loop heat transfer fluid to theambient air.

In use, a recirculating, evaporative fluid is distributed over theentire plan area of and traverses via gravity over the entire externalsurface area of the heat transfer, fluid carrying, closed loop, indirectheat exchanger 10, enabling the interactive link between both heatexchange methods via sensible heat transfer, indirectly absorbing heatfrom the heat transfer fluid.

The heat absorbed by the external, recirculating, evaporative fluid isdirectly cooled via evaporation by the entering ambient air which movesin a counter flow direction. After the recirculated, evaporative fluidtraverses over the indirect heat exchanger and thru the air plenumsections it reaches its lowest temperature when collected in the basinto be delivered back to the evaporative fluid distribution system.

The closed loop, indirect heat exchanger 10 is arranged similar to anair-to-refrigerant heat exchanger (e.g. evaporator) tube bundle sectionand typically utilizes less than 1″ diameter, multi-macro caliber(outside diameter) tubes 22, “canes” 24 and “hairpins” 28, with,partially or without internal enhancements, spaced optimally in bothhorizontal and vertical directions to minimize air and fluid sidepressure drops, maximize overall heat transfer while facilitating properinternal fluid drainage. In the case where the internal heat transferfluid exists in two-phases during operation, internal, inlet tubetemperatures can significantly exceed the operating saturationtemperature of the two phase fluid. Single phase heat transfer fluidsalso experience significant temperature differentials in the tube bundle20 between the inlet connection 12 and header 14 and outlet connection16 and header 18. Moreover, and as a result of this arrangement, theupper rows of the indirect heat exchanger 10 are exposed to hightemperature refrigerant and, thus, are susceptible to acceleratedcorrosion. To resist such corrosion, the upper rows of the indirect heatexchanger 10 incorporate a higher-corrosion-resistant material than thelower rows. For example, 316 or 316L SST grade material or similar couldbe used for the upper rows, while 304 or 304L SST grade material orsimilar could be used for the lower rows, to meet site specificapplication requirements and significantly inhibit corrosion due tooperating temperatures which accelerates this type of activity. It iswell known that 316 stainless steel has improved corrosion resistanceover 304 stainless steel due to the addition of more nickel andmolybdenum. As compared to 304 stainless steel, 316 stainless steelresists corrosion and subsequent pitting by most chemicals, includingchloride and chlorine.

Normally, the number of upper rows that incorporates ahigher-corrosion-resistant material is less than the number of lowerrows that incorporate a lower-corrosion-resistant material.

Although the example provided uses just two different tube materials, itis contemplated that any number of different materials could be used forthe tubes of a single tube bundle. For example, three differentmaterials could be used: the highest-corrosion-resistant (and likely thehighest cost) material could be used for the upper rows, a lower cost,but still high corrosion-resistant, material could be used for themiddle rows, while the lowest cost and lowest-corrosion-resistantmaterial could be used for the lower rows. At the extreme, each passcould utilize a different material. Materials used in the tube bundlecould be chosen from at least the following: copper or copper alloys,including but not limited to as Cu.DHP, CU K65, CuFE2P, C19400; steels,including but not limited to P195TR2, ASTM A214, and ASTM A214M;aluminum or aluminum alloys, including but not limited to AA3003 andAA3110; titanium; nickel and nickel alloys, including but not limited tonickel base alloys; ceramics; plastic or plastic compounds andcomposites, including but not limited to PS, PVC, PE, polymer ceramics,polyamid, polyatic acid PLA, PEEK plastic; and carbon-based materials,such as CFK, CFRP, and glass-carbon natural fibres. Any combination ofthese and other materials could be used, such as: stainless steel withcopper or copper alloys; copper with copper allows; aluminum withaluminum alloys. In addition, it is contemplated that return bends couldcomprise a different material than the straights for example, if thematerial used for the straights are not easily bendable.

Moreover, although the example provided uses a single homogeneousmaterial for the upper rows, and a different, single homogeneousmaterial for the lower rows, it is contemplated that each row of tubescould comprise multiple materials. As an example, the upper rows most atrisk for corrosion could have a base of 304 or 304L SST grade materialthat is coated with a different material, such as epoxy, zinc, Teflon,nickel, or tin plating, that has a higher resistance to corrosion.

The method of manufacture of the heat exchange device in FIGS. 1-6easily accommodates the use of multiple materials. As shown, the tubebundle 20 is manufactured using four different types of tube segments22, 24, 26, 28 that are connected together at welds 30 or otherequivalent connections (e.g., brazed connections): “straight tubes” 22for the first and last passes, “canes” 24 (generally shaped like a “J”)for the second and second to last passes, which are separated byalternating “return bends” 26 and “hairpins” 28 (both generally shapedlike a “U”).

In the embodiment shown, a high corrosion-resistant material (316L SST)is used for the first two tube passes (i.e., the first straight tube 22and the first cane 24). If it was found that the first four tube passeswere subject to a high risk of corrosion, the first return bend 26 andfirst hairpin 28 would also be fabricated using the highcorrosion-resistant material. If only a single tube pass was subject toa high risk of corrosion, the first straight tube 22 would be the onlytube fabricated from high corrosion-resistant material. Rearranging theconfiguration of canes, “hairpins”, and elbows enables fabrication fromhigh corrosion-resistant material for the first elbow connected to thefirst straight tube. If an odd number of tubes greater than one weresubject to a high risk of corrosion, additional canes 24 could be usedbefore transitioning to return bends 26 and hairpins 28.

Although only a single example of a heat exchanger 10 is shown, multipleheader quantities and configurations, quantity of tubes in the airdirection and/or tube bundle width, circuit patterns and resultant,variable circuit lengths can be easily configured which enables fluidflow downwards or upwards, to achieve optimum heat transfer whilemaintaining a minimum, internal fluid pressure drop. This device 10 canalso be used to accommodate different heat transfer fluids within thesame tube bundle. The heat exchange device 10 is intended to be used asan evaporative gas cooler, condenser or fluid cooler or combinationthereof and may be operated in a dry mode.

It is contemplated that the inventive features of the heat exchangedevice 10 can be incorporated in other types of heat exchangers. Indeed,although the inventions described and claimed herein have been describedin considerable detail with reference to certain embodiments, oneskilled in the art will appreciate that the inventions described andclaimed herein can be practiced by other than those embodiments, whichhave been presented for purposes of illustration and not of limitation.Therefore, the spirit and scope of the appended claims should not belimited to the description of the embodiments contained herein.

We claim:
 1. A heat exchange device comprising: a multi-pass tube bundlewith at least a first pass and a subsequent pass; the first passcomprising a first material and the subsequent pass comprising a secondmaterial; and, the first material being different from the secondmaterial.
 2. The heat exchange device of claim 1, wherein at least onetube defines both the first pass and the subsequent pass.
 3. The heatexchange device of claim 2, wherein the at least one tube is defined bya plurality of connected tube sections.
 4. The heat exchange device ofclaim 3, wherein the tube sections are selected from the group includingstraight tubes, canes, return bends, and hairpins.
 5. The heat exchangedevice of claim 1, wherein the first material has a greater resistanceto corrosion than the second material.
 6. The heat exchange device ofclaim 5, wherein the multi-pass tube bundle defines an evaporativecondenser adapted to discharge heat to an external, recirculating,evaporative fluid.
 7. The heat exchange device of claim 1, wherein thefirst material is 316/316L stainless steel and the second material is304/304L stainless steel.
 8. The heat exchange device of claim 1,wherein the first material is disposed at an outer surface of the firstpass of the tube and the second material is disposed at an outer surfaceof the subsequent pass of the tube.
 9. The heat exchange device of claim1, wherein the first material has a higher concentration of nickel,molybdenum, or both nickel and molybdenum than the second material. 10.The heat exchange device of claim 1, wherein the first pass of the tubeis the only pass of the tube comprised of the first material.
 11. Theheat exchange device of claim 1, wherein the tube has a second passcomprised of the first material.
 12. The heat exchange device of claim1, wherein the first pass of the tube is connected to an inlet of themulti-pass tube bundle and the subsequent pass of the tube is connectedto an outlet of the multi-pass tube bundle.
 13. The heat exchange deviceof claim 1, wherein a first tube section defines the first pass and asecond tube section defines the subsequent pass.
 14. The heat exchangedevice of claim 12, wherein the first tube section and the second tubesection are connected in series.
 15. The heat exchange device of claim 1further comprising a first group of tube passes and a subsequent groupof passes, wherein: the first group of tube passes includes the firstpass and the subsequent group of passes includes the subsequent pass;and, each tube pass in the first group of tube passes comprises thefirst material and each tube pass in the second group of tube passescomprises the second material.
 16. The heat exchange device of claim 14,where a number of tube passes in the first group of tube passes is lessthan a number of tube passes in the second group of tube passes.
 17. Theheat exchange device of claim 15, wherein the first group of tube passesare the only group of tube passes comprised of the first material. 18.The heat exchange device of claim 15, wherein the second group of tubepasses comprises all remaining tube passes of the multi-pass tubebundle.